1. Technical Field
This invention relates to analog-to-digital converters for converting an analog input signal to a digital output representation and, more particularly, to an asynchronous successive approximation analog-to-digital converter.
2. Discussion
Analog-to-digital converters are commonly used in a wide variety of applications for converting an analog signal to a digital representation thereof. One common method of providing analog-to-digital conversion is with successive approximation. Successive approximation generally employs a comparator, a digital-to-analog (D/A) converter and a successive approximation register (SAR) and additional electronic devices such as clocks, flip-flops and latches.
A conventional successive approximation analog-to-digital converter is essentially a synchronous device that requires at least N clock cycles to provide an N-bit conversion. As a result, a four-bit successive approximation conversion would generally require at least four clock cycles. In addition, the typical successive approximation converter is a relatively slow device because it does not make comparisons with the input signal simultaneously as is generally accomplished with a flash converter.
Another method of providing analog-to-digital conversion is with the use of a flash converter. A conventional analog-to-digital flash converter generally employs 2.sup.N comparators in conjunction with an accurate resistor network. As such, the flash converter generally requires at least 2.sup.N electrical components including the 2.sup.N comparators to perform an N-bit conversion. As a result, the relatively large number of electrical components that are required may lead to a very high circuit complexity, especially for high bit converters.
It is therefore desirable to obtain an analog-to-digital converter that is asynchronous and therefore does not require any clock timing. In addition, it is further desirable to obtain such an analog-to-digital converter that requires fewer electrical components than the conventional flash converter.